


The Reason Why

by JDGambit



Category: Harry Potter - J. K. Rowling, Katekyou Hitman Reborn!
Genre: Actually Immortal Skull, Adult Arcobaleno, Crossover, Depression, Genderfluid Mammon, Gross petnames, Hey ho its, In a way, Kinda, M/M, Mafia Boss Sawada Tsunayoshi, Magic Revealed, Master of Death Harry Potter, Not Epilogue Compliant, Secret Relationship, Squib Mammon
Language: English
Status: In-Progress
Published: 2016-12-30
Updated: 2018-04-02
Packaged: 2018-09-13 08:36:09
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,866
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9115225
Author URL: https://archiveofourown.org/users/JDGambit/pseuds/JDGambit
Summary: Everyone is shocked and confused. Tsuna's confused. Dino's confused. Even Reborn's confused.Featuring Mammon with a bad case of hero worship.





	1. Chapter 1

**Author's Note:**

> i dont know what this is. i really have no idea. this came out of nowhere im so confused. i read so much fanfiction bout skull being harry that i was like nah what if they're all romantical together. and then this happened. sorry.

The calm that settled over the mafia after the Vongola’s shift in power was a relief for the entire underground. It was a feeling that no one wanted to give up. The older Bosses knew, however, that the peace couldn’t last for long. When the Vongola Decimo called a meeting of his allies, the underground quaked in fear. No one knew what to expect from the young boss. No one would miss their chance to find out.

Personally, Reborn was feeling a bit miffed Tsuna didn’t give him any forewarning. Shouldn’t that idiot know that, as his tutor, he would be the first to be pestered for information? As things were, he entered the elegantly decorated meeting hall with the rest of the restored arcobaleno. There was something about the way eyes followed nervously that spoke to their ominous aura. Even the Lackey, Skull, who trailed in behind the rest, cut an intimidating figure. 

The group of seven— Colonello, Lal, Mammon, Verde, Fon, Skull, and himself, were led to the table nearest the three where the Decimo, his guardians, the Varia, and CEDEF were seated. The other seats were filled slowly, though no one dared to linger where they shouldn’t. By the time the movement in the hall settled there was only one table left empty. Moments later, a group of figures hidden in billowing cloaks guided by no one made their way to the table. Every step they took spread a wave of uneasiness further over the hall.

Reborn looked at Tsuna. Though the young man didn’t look worried in the least there was a certain edge in his smile. A warning against misbehavior but for whom? He could see Colonello struggling to keep his hand from his concealed weapon. Something about that group was seriously grating at him. 

When the hooded figures were settled, Tsuna stood. His eyes, glowing that fiery orange, stared down his guests. Something proud swelled up in Reborn’s chest. This student of his had grown well. Even the stupid bronco, sat at a table with as many of his men as it could fit, didn’t take as well to his teachings. 

“One week ago, I received contact from a society that has been largely unknown to our world, civilian or otherwise,” said the Decimo. Skull and Mammon froze at his words. Largely unknown, Reborn could see, was an important distinction. Mammon he could understand. They knew almost everything and what they didn’t, well, that was always resolved quickly. There was no question they knew about this hidden society. Skull, however. How did a civilian like him know of a thing like this? There was something incredibly irritating about the weakling knowing something he didn’t, especially something of this apparent scale.

“The representatives of this society alerted me to the fact that our societies have certain similarities. After centuries of staying hidden, they wish to open communication between us. I invited a small delegation,” he gestured pointedly at the table of cloaked figures, “to join this meeting today to begin this process.” A buzz of speculation ran through the hall. Reborn made sure to note that, besides the Vongola tables, Mammon and Skull were the only ones whose curiosity outweighed their apprehension. Even he was tense in his seat.

“I will tell you now if only to ease your worries, that these guests have sworn vows to cause no harm while here unless in self-defense. Please, do not worry, I would not allow harm to fall on my allies in my own home.” Tsuna looked over his guests one more time freezing them in their seats. His eyes met Reborn’s and it took almost all his power not to smirk at the mischief in the Decimo’s gaze. The brat was looking forward to his reaction.

“I’ll now turn over the floor to our guests, the Magic Disclosure Squad from the Wizarding World.” The what? Skull and Mammon leaned forward in their seats as the group stood and removed their cloaks. 

Seven unfamiliar faces gazed about the hall. They were a group of mismatched ages and sizes dressed in ornately embroidered robes. It was easy to see, even in the short time it took for them to get in place, that they were a complete set of guardians. They weren’t all harmonized to the sky but they were protective all the same. 

The stern looking woman wearing glasses was older than anyone else in the hall by at least half a decade. Her flames weren’t active but there was a distinct mist aura surrounding her. The next oldest was a tall black man with a thousand-watt smile. He looked to be in his mid to late forties and, even as an inactive rain, his presence was soothing and steady. The next four were around the same age: late twenties to early thirties. Kids really. Two men, both blond, one tall the other pointy, and two women, a freckled redhead, and a bushy brunet. They were the sun, clouds, storm, and lightning respectively in the group. Once again, none of their flames were active in the slightest. All six of them surrounded the sky.

Unlike the others, the sky was an actual child— barely older than Tsuna. He was nineteen at the very most in Reborn’s expert opinion. He was short and thin, his hair was a wild, black mess and his eyes glowed an eerie green behind his glasses. There was a scar like lighting on his forehead. Even if he hadn’t been leaking extraordinarily pure sky flames, the way he was surrounded would have given his type away. 

The boy looked over at the table of arcobaleno sharply. There was something in his gaze that was penetrating and cold even as he gave an easy smile. Through his own alarmed and rapid heartbeat, he could barely hear Mammon’s startled inhale as the boy looked pointedly at Skull. His eyes softened and he winked. Everyone was staring at the pair, even the Decimo. As such, the whole hall was witness to the kiss Skull blew back. Had he been anyone other than the greatest hitman in the world, Reborn may have gaped at the scene. Colonello, Dino, and other nameless Mafiosi had no such titles to still their expressions. Fon’s face was still if only because of decades of training. Even Tsuna had briefly snapped out of his ‘boss persona’ and watched with wide eyes. How nostalgic. As if unaware of the commotion he’d instigated, the boy joined his companions. 

Strangely enough, it wasn’t the elders of the group that moved to speak. They were both leaders in their own right but they stayed where they were. Instead, it was the youngest of the bunch. Perhaps not so odd, actually. He was a sky after all. Speaking of sky… Skull’s eyes never left the boy. Reborn could see it, the harmonization between them but, when on earth did that happen? How did the lackey know someone like that? It all made his head spin. 

The boy stood confidently. The attention he drew didn’t seem to distract him in the least. His composure was commendable. The boy’s voice was rough as he spoke as if it was rarely used. It was neither low nor high in pitch; just rough. It wasn’t at all unpleasant to listen to. Skull seemed soothed by it.

“First off, I’d like to thank our host for hearing out me and mine. Allowing us here is an honor that will someday be paid in full. I’m not usually one for speeches but today itself can be considered a bit odd.” He smiled at the hall and ignored the looks of suspicion.

“The people standing around me are my friends and teachers, most of whom I’ve known of since I was much smaller than I am now. The lovely woman to my far right is my former teacher and Headmistress, Minerva McGonagall. Next to her is Lord Draco Malfoy head of the Ancient and Noble House of Malfoy and directly next to me is Hermione Granger, my right hand and long-time best friend. On my other side, my left hand, Neville Longbottom, one of the loyalist men I’ve had the pleasure to know and to him is Ginny Weasley, youngest of seven and toughest of the bunch. Finally, on my far left is a good friend and the man who gave us permission to accept this opportunity, Kingsley Shacklebolt, Minister of Magic.” The boy waited a moment to let the information sink in and give his voice a rest. 

The first question that came to Reborn’s mind was why is the boy’s best friend in her thirties? Was she his babysitter when he was young? No, probably not. There was something about the boy. Something about the steel in his stride and fire roaring eyes. That and his interaction with the Lackey. There was something wrong with him. The boy took a deep breath preparing himself for his own introduction. Skull stifled a snicker knowing what was coming. 

“I am Lord Harry Potter-Black, head of the Ancient and Noble houses of Potter and Black, and,” he twitched. Skull laughed outright, “the Man-Who-Conquered. My companions and I are from a society that lives hidden alongside both the civilians and mafia. We call our society the Wizarding World. The name, I’m afraid, is entirely literal. Us seven who stand in front of you are called wizards and witches. Where the mafia has people capable of activating Dying Will Flames we are a society of people capable of manipulating the energy we’ve come to call Magic.” 

Loud shouts of disbelief tore through the meeting. Had it not been for the stiff line of Mammon’s shoulders and the dopey smile on the weakling’s face, Reborn might have been inclined to join in the chaos. It was rather unbelievable; a secret world of magicians who suddenly want to share themselves with the world. Everyone in the hall froze as the Decimo knocked lightly on his table. His eyes narrowed dangerously.

“Let him finish.” No one dared argue. Harry, who still seemed unaffected by the clamor, nodded thankfully at the other young man.

“In the past few years, researchers such as my right hand and our Department of Mysteries have found many connections between your flames and our magic. They have even gone so far to conclude that both came from a single source and are like cousins energy-wise. Because of this, the Ministry of Magic has decided to welcome the flame active and their families into our world should they wish it. Everyone here is eligible to join us.” Harry and his right hand, Hermione, raised their hands. Decorated, pointy sticks shot out from their sleeves and into their hands. With a wave, a small stack of books appeared on each table. In front of Skull, a single rose appeared. He was the only one to receive such a gift. 

“These books are a gift from us to you. These are what you could call an introduction to our world. A brief look at our history, capabilities, and creatures. Whether you read them or not is entirely up to you. Should you like to know more, feel free to ask. Me and mine will be in the area for a while.” He bowed lowly, an action that was mimicked by the rest of his group. “Thank you for hearing us out.”

With that, the wizard sand witches sat back down. All except Harry who instead turned to face the arcobaleno. As he walked, the hall tensed further. He was a man on a mission and showed no signs of faltering. Leon was calm, sensing no danger, but Reborn was too tightly wound to notice. 

A loud crack echoed and the boy was gone. Another and suddenly he was right behind Skull’s chair. Had he waited, Reborn would have noticed Hermione and Nevil shaking their heads and complaining about Harry’s show-off tendency’s. If that had happened, he probably wouldn’t have pressed his gun into the boy’s throat. Colonello might not have jabbed his weapon into his side. Mammon froze as they accosted the wizard. Skull didn’t even turn around, just twirled the rose between his fingers. 

“Skull, my lovely phoenix of a man, can you get these guns off of me? They’re quite uncomfortable.” Skull scoffed on that annoying high voice of his. He turned around and glared at Harry. 

“That’s what you get for not telling me you were coming,” he exclaimed, “you can get riddled with holes for all the Great Skull cares, Sweetheart.” Reborn watched as the boy pouted like a child denied chocolate. It didn’t seem to fit his face but from the way Skull’s eyes softened, he didn’t mind. This was weird. Cautiously, he and Colonello eased the pressure of their guns. 

“Please, Kitten? Not even a hello?” He begged. It was hard to believe this pitiful boy was the same one who had thrown the hall into chaos minutes earlier. 

“If you want your hello so badly, get passed Reborn and Colonello yourself. Anyone who knows you knows you sure as hell didn’t write that speech. It had Hermione written all over it. You could at least do this on your own. You’re a big boy, sweetheart.” This Skull, the one who was scolding that powerful sky, was so different than the one Reborn and the other arcobaleno knew. He was so relaxed. 

Harry sighed. With a flick and a twist of his wrist, both of his attackers’ chairs rammed into the back of their knees. They didn’t fall but the space they left as they started was more than enough for him to get through. Quick as a flash, he wrapped his arms around Skull who gladly returned the affection.

“Hello, Sweetheart,” Skull muttered into Harry’s neck. The pair, trapped in their own little lovey-dovey world, didn’t notice the shocked and uncomprehending stares being shot their way. Reborn, though he wasn’t as unbalanced as a large portion of the hall, would admit to some disorientation. Who knew the stuntman had a sky? Or could hold someone so tenderly? Tsuna and his guardians clearly had not been informed of this beforehand. The magical group seemed unperturbed as ever. Mammon’s gaze was fixed solely on the wizard’s back. The Man-Who-Conquered; such an impressive title for someone so young. A title that obviously had their mist captivated. 

Several moments later, the stunned silence was broken by a pointed cough from the tall blond, Neville. The hugging pair broke apart, neither looking embarrassed in the slightest. He’d let them have their moment. Reborn hadn’t even been the one to interrupt them. Skull was now completely available for interrogation. He turned a glare at their audience. They turned away without hesitation for fear of the consequences. 

“Lackey, who is this?” The wizard turned cold eyes on Reborn. He was like a snake poised to bite at any second and he felt a tendril of fear twine around his spine. Though it hadn’t been said with any malice, the boy was powerful and clearly didn’t like skull’s nickname. He calmed in an instant as Skull patted his shoulder. 

“This is Harry, my lover.” He pulled Harry close. “Oh, and the reason why I’m immortal!” No one was sure exactly how to respond to that.


	2. Chapter 2

**Summary for the Chapter:**

> How things began.

**Notes for the Chapter:**

> listen. listen. I know it’s been a while. like... a hella long while. enjoy?

For most, death is a nebulous concept that can’t be fully grasped until it comes for them. However, for the many-titled Harry Potter-Black, death was much more than that. It was tangible, sentient, a constant presence and yet impossibly out of reach.

The years after the death of his prophesied rival were hectic; a constant hustle and bustle which he wanted little to do with. There were highs, such as the marriage of his two best friends, and lows, like the seemingly endless stream of funerals and burial ceremonies that lasted for months and then trickled on for the better part of the year. It was because of his constant on-the-go lifestyle that Harry, and even his closest friends, failed to notice the oddity happening to him until he was twenty-five years old. 

Harry lounged in the sitting room of 12 Grimmauld Place, his godson, Teddy, whom he was babysitting on one of his rare days off, played on the rug with a set of floating blocks which gave off brightly colored sparks when they collided. A picture rested on the fireplace mantle across the room, inconspicuous in it’s plain wooden frame. It was a momento from graduation; a simple shot of him and his friends on their final day at Hogwarts. He was nineteen in the picture; his smile wide as he beamed at his friends. They were all so happy to be alive. They were so young.

The past half decade or so had been hard on everyone. Hell, the past decade had been hard and time couldn’t help but show its passage. Small furrowed lines had grown around Hermione’s eyes, born from all the days spent frowning at books and parchment down in the department of mysteries. New scrapes and scars showed up daily on Ginny, a tough as nails quidditch player and Ron’s hair had begun thinning around the temples; a combination of genes and the stress of being an auror to blame. 

As he stared at the lively image, however, a realization struck him across the face. It filled him with a sick dread so strong he had to fight the urge to gag. Carefully stepping around his giggly godson, he snatched the frame off the mantle with trembling hands. He traced his own face with a finger, hoping to be terribly mistaken. As sad green eyes met his and gave a small, defeated shrug he knew his hope was nothing more than the pleading wish of a desperate man. 

Harry Potter-Black wasn’t aging.

After several minutes of staring into fireplace, and an especially enthusiastic squeal from Teddy, the shock wore off and he found himself unable to be truly surprised. On some deep subconscious level, he must have known. In fact, he could probably even pinpoint the moment when it started. He recalled, with dread in his bones, a morning two weeks after the final battle, when a wand he’d broken with his own hands appeared before him as he ate his breakfast of fruit and toast. Even still it refused to leave no matter what he did. And since that day… 

Harry couldn’t remember the last time he’d needed a haircut. His face was as smooth and hairless as it had ever been and far too youthful to belong to a man of his age. Even his clothes, bought on his seventeenth birthday in the height of his growth period, and made of spell-resistant dragonhide which, thus, couldn’t be spelled to grow with him, still fit like a glove. 

Rationally, he knew it could all be explained away easily. He could be an especially hairless man whose growth was stunted due to childhood malnutrition and had especially stubborn hair which had a mind, or magic, of its own. But he knew. He knew. There was no point lying to himself any further. 

Resigned, tired, and too old for his age, he set the picture back on the mantle, picked up his godson, and flooed Hermione.

 

Tests upon tests were conducted on him in the department of mysteries and he found there were certain elements of his new-found strangeness that he enjoyed. He healed exceptionally fast; “Scarry quick,” according to Ron and there was a level of strength and accuracy to his spellwork that he didn’t know he possessed. The downsides, however, were blatant, in his face, and frankly impossible to ignore. He couldn’t age. He couldn’t die. He would live to see everyone he loved grow, wither, and perish. He would attend a thousand funerals and then a thousand more and still be waiting for the next one. 

Maybe he was being melodramatic, but he couldn’t bring himself to care. He was drowning in his own future and he. Couldn’t. Breathe.

 

Years passed by and Harry watched in a haze as the world continued around him. Though he had many frequent visitors, it was a rare occurrence that he left Grimmauld Place. Teddy grew older and wiser with every passing day, month, and year and, in the blink of an eye, he entered Hogwarts. Ron and Hermione had a child, and then another, and settled into a cottage not all that far from the Burrow. Ginny was traded to another team, quickly took the captain seat, and lead them to three consecutive World Cup wins. Minerva McGonagall, having reached an age she deemed ‘too old’ to be dealing with hundreds children and nosy bureaucrats trying to run her school for her, retired from her position as Headmistress of Hogwarts. Even Draco Malfoy, once cast aside and shunned, slowly built himself back up to a respectable place in society. And, through it all, Harry watched and listened silently, falling further and further into the depths with every breath.

It was the morning of his thirtieth birthday and enough was enough.

Storming through the floo of Grimmauld Place in a blaze of sparking green flame, Hermione Granger posed an intimidating figure. She was a mane of wild hair and shrewd, narrowed eyes which cut across the room and pierced straight into Harry’s soul. For the first time in a very long time, he looked at her properly. Having reached the age where magic folk’s aging slows to a crawl, to aid their extended life spans, she hadn’t changed all that much despite all the years passed. There was a short, thin, silvery scar on her chin now, perhaps from an experiment gone wrong at work, and a tiredness that clung to her like a damp cloak. 

“Harry James Potter,” she announced as she took in his disheveled appearance, “put on some clean clothes for fucks sake.” She turned on her heel and took off into the house leaving Harry wide-eyed in her wake. Knowing better than to test her patience, Harry wandered up stairs, noting as he passed the the dust collected on the picture frames. 

His room was a mess. Some would go so far as to call it a catastrophe. Clothes were strewn across the floor and on all the furniture. Not even his bed was free from the clutter. When was the last time he’d actually slept there and not simply fallen asleep on the couch downstairs? His clean clothes were hidden away in the back of his wardrobe, unworn for years. The sweater and jeans he pulled out were stiff with dust and smelled stale but he threw them on nonetheless. If he took too long up there, Hermione would without a doubt come up after him and, as he looked around at his disastrous living conditions, he realized he didn’t want her to see how shameful he’d become. 

Hermione sat at the dining table; a stack of papers in one hand, a small wrapped package resting under the other on the table. As Harry entered the room she looks up from the papers. She gave a nod as if marking something off a checklist only she could see, then gestured for him to sit. She pushed the package across the table. 

“Happy birthday, Harry,” she said with a smile. The tiny lines around her eyes crinkled. He wished his own eyes had lines like that. He thanked her quietly, grimacing at how harsh his voice sounded from disuse. He unwrapped the gift gingerly, careful not to tear the paper, and revealed a red bottle cap with a gold ‘X’ painted on top and a shrunken bag filled with the unknown. Wordlessly, the stack of papers was passed over the table. There was… a lot of words on those pages, far more than he’d read in ages. Truthfully, it took a couple minutes for his brain to make sense of what he was seeing. The unsurprised and endlessly patient look on Hermione’s face made him consider that perhaps he was in worse shape than he’d thought.

At the top of the first page in bold, black print read ‘Temporary Head of House Relief’. His breath caught in his throat. He looked at his best friend helplessly, unsure if he was reading what he thought he was. Her eyes were hard, but not unkind, as she nodded at the papers, all but demanding he continue. He flipped through the papers and found the next titled page; ‘Muggle Identification Application’, it read. A few pages later he found the ‘Portkey Registration’ form. An image was forming in his mind. The bottle cap, now clearly a portkey, and bag on the table, surely filled with clothes, food, and shelter, looked so much heavier all of a sudden. As did Hermione’s unwavering gaze. 

“‘Mione, what is all this?” He asked softly.

“We love you, Harry. I need you to know that, alright? I love you, Andy and Teddy love you, Ron loves you and so do all of the Weasleys. Neville and Luna, Dean and Seamus, Kingsley, McGonagall, we all love you to absolute pieces. We’ve given you a lot of space these last few years. We let you deal with this immortality nonsense on your own because that’s clearly what you wanted and we respect that. We gave you your time to work through this. Probably too much time, to be honest, but, well, if there’s anything you have plenty of it’s—,” she cut off looking regretful for a moment. 

These years had been hard on her. The endless hours she spent down in department of mysteries trying to find a way to kill her best friend had certainly taken their toll, especially as each theory was thrown out as impossible. Harry could remember, it those first few months, how certain she had been in all of her work. He remembered watching that certainty falter within the year. He secluded himself soon after, not wanting to find out exactly how much more she’d been beaten down. No matter what, though, Hermione Granger was made of steel, grit, and at least a thousand books. Hermione Granger never gave up. 

“You don’t need to be better right this second, Harry. Whether or not this plan works, however, you cannot keep living like this. It’s unacceptable. Honestly, if it was possible, I’m certain you’d have died by now. Do you understand that?” Something painful gripped Harry’s chest at the tortured expression he wore. He was hurting her. He was hurting so many people. 

“I’m sorry,” he whispered only to be met by a frustrated growl. 

“Thank you,” she bit out, “but I didn’t come here for an apology! I came to help! And, yes, Harry,” she spit, pinning any protest he had to the ground, “you do need help.” And she was right.

The walls of Grimmauld Place had become familiar in the most haunting of ways. He, himself, became a ghost of its halls, imitating an afterlife he’d never truly experience. 

“I need to leave,” he said to himself. He gripped the edge of the table, his knuckles turned white. Deep in the depths of his consciousness, where he’d long been silent and still, submitting to the dread that chained him, Harry stood; still shrouded in darkness and unable to breathe, but finally looking toward the surface. 

“You need to leave,” Hermione agreed easily, “and these forms will make sure you can.” She snatched back the papers and laid them down in three stacks. “This one,” she said pointing at the first stack, “will temporarily put someone of your choosing I charge of your house holdings. This includes any Wizengamot seats, stocks, businesses, and bank vaults. Your standee can’t make any major decisions, they’re just there to make sure nothing gets messed up. You would still be head of house but would be relieved of your duties for a period of time between one month and five years.”

“This next one,” she continued after a breath, “will make sure everything is in place legally on the muggle side of things. You’ll receive a copy of your birth certificate, an ID card, and passport. You also get a way to access your Gringotts vault outside of the wizarding world. Finally,” she tapped the last and smallest stack lightly, “I believe this is self explanatory. It’s just legal documentation for that portley you have there.” She scoured his face for any sign of comprehension. “You find a standee, get a passport, register that portkey, and you’re free, Harry.” When he gave no sign of replying, she reached out for his hand, gently prying it from the table. 

“Will you think about it? Please?” There was a hint of desperation in her voice that he absolutely despised. It made a fury burn deep in his gut where emptiness had once grown. He was the reason why she was so tired; so desperate. How dare he hurt her like this? There was no thought needed. 

He shook his head slowly but, before Hermione’s face had a chance to fall, Harry summoned a quill and ink and began filling out the forms.

**Notes for the Chapter:**

> No skull? No sign of khr at all? Listen. I don’t know what I’m doing for the most part but this’ll all fit together. Probably. Harry’s gotta go through some shit first.  
> Was this what you were wanting? Yes? No? Who knows.

**Author's Note:**

> will there be more? i have so many more ideas for this crossover. im sure there will b.


End file.
